Soil conditions and formulated fertilization for major crops in Fujian Ⅱ. Sufficiency indices of alkali-hydrolyzable N,olsen-P and available K in Soil

This paper illustrates a system,based on the field tests completed,that divided soil fertility into high,medium and low grades and established indices to show the degree of sufficiency or deficiency on available N and P and K in soil for the major crops in Fujian.The results indicated that the logarithm model fitted best for calibrating the alkali-hydrolyzable N,the exponential model for Olsen-P and power model for available K.The critical value of the soil's available nutrient was affected by crop nutrient requirement and planting time.In the mountainous area,the critical values of alkali-hydrolyzable N,Olsen-P and available K for the early-season rice were 217,26 and 116 mg•kg-1,respectively;for the late-season rice,211,19 and 105 mg•kg-1,respectively;and for the mid-season rice,230,24 and 109 mg•kg-1,respectively.In the coastal area,the critical values of alkali-hydrolyzable N,Olsen-P and available K for the early-season rice were 193,18 and 105 mg•kg-1,respectively;and for the late-season rice,183,17 and 82 mg•kg-1,respectively.For the upland crops,the critical values of alkali-hydrolyzable N and Olsen-P and available K for sweet potatoes were 141,20 and 135 mg•kg-1,respectively;for potatoes,207,35 and 97mg•kg-1,respectively;and for peanuts,123,24 and 87 mg•kg-1,respectively.The soil's available nutrient evaluation showed that,based on soil's alkali-hydrolyzable N,93.8% of the paddy soil were of medium grade,and 89.5% of the upland soil samples were of low grades.On the basis of Olsen-P,62.9% of the paddy soils,while 59.9% of the upland soil samples,were of high grade.When the available K was taken into account,66.5% of the paddy soils were considered medium and 87.4% of the upland soils low fertility.These results were in agreement with the conclusions drawn from field experiments that showed N and K high fertilizer efficiency and P lower efficiency.